1. Field of the Invention
The present invention relates to a method of consolidating some parts made of an appropriate "Ni--Ti alloy" with other constituent members so as to form a pair of spectacles, wherein the "Ni--Ti alloy" parts may include a bridge, a cross bar, temples (or earpieces) and the like desired to have a property of shape memory. The other members may be skeleton members such as lens rims, hinge webs or the like that are made of a "titanium material" not being of such a shape memory property. The "Ni--Ti alloys" are substantially composed each of nickel and titanium and are of the so-called "super-elastic" property. The other term "titanium material" defines herein a material selected from the group consisting of pure titanium and its alloys that are weldable and/or brazeable depending on conditions employed.
2. Prior Art
Generally, it is difficult for articles made of Ni--Ti alloys or some titanium materials to be brazed in a simple manner to each other or to any other metallic article. Therefore, some cylindrical joint pieces 22 made of a weldable metal (such as pure titanium) as shown in FIG. 8 have been used to get around such a difficulty. In the illustrated example, a bridge 21 is a Ni--Ti alloy part included in the framework of a pair of spectacles. One end of this bridge 21 is fitted in a bore 23 of the joint piece 22, with this bore having a blind bottom. Subsequently, a cylindrical wall of the joint piece 22 will be pressed or `caulked` strongly in a centripetal direction to set the bridge end in place. Such a caulked cylindrical joint piece 22 may then be resistance-spot or butt resistance-welded to a lens rim 24 or the like made of a titanium material.
However, it is inevitable that small crevices or interstices exist between the Ni--Ti alloy part 21 and the inner periphery of the caulked joint piece 22 which is being resistance-welded to the lens rim 24. A high voltage will be applied to and through the part 21 and the piece 22 across the interstices, thus resistance welding them together at an elevated temperature. Electric sparks are likely to be emitted in the interstices due to the high voltage, thereby bringing about deformation of or cracks 25 in the joint piece. As a result, connection strength of the caulked members has often been impaired to an intolerable degree.